#!/bin/bash
echo "This is bash"   && :  $(echo "This is Bash as well")
echo "some calculus:   $((12*456))"
if [ -f "x" ];    then
            echo "This is something!"
fi

${xyz:=345}
-----
#!/bin/bash
echo "This is bash"   && :  $(echo "This is Bash as well")
echo "some calculus:   $((12*456))"
if [ -f "x" ];    then
            echo "This is something!"
fi

${xyz:=345}